Abstract The heat shock protein (HSP) gp96 is immunogenic. Depending on which antigen presenting cell (APC) is targeted by gp96 in the extracellular environment, these immune responses can be opposingly of the Th1 or Treg type. These immune responses have been harnessed for the immunotherapy of cancer and infectious disease or autoimmune disease respectively. We have shown that the gp96 receptor, CD91, is expressed by conventional dendritic cell (cDCs) which allows for cross-presentation of the antigens chaperoned by gp96 and for provision of co-stimulation for Th1 responses. We have recently uncovered CD91 expression on plasmacytoid dendritic cells (pDCs). There is currently no information on how pDCs influence gp96-mediated immune responses and specifically, how Treg responses are modulated. Our hypothesis is that engagement of pDCs by gp96 via CD91 leads to intracellular signaling and upregulation of molecules associated with priming and stabilization of Treg function. Our studies here explore how gp96 engages the various APC populations in situ, the intracellular signaling with pDCs, and the phenotype of gp96-activated pDCs in the context of priming Tregs and enhancement of their function. This pathway has consequences not only for tumor development and infection but in autoimmunity, and in immunotherapy of these diseases.